1. Field of Invention
The present invention relates to a lock-up device, particularly to a lock-up device for a torque converter, which is configured to transmit torque from a front cover to a transmission-side member through a turbine of the torque converter.
2. Background Information
In many cases, a torque converter is provided with a lock-up device for directly transmitting torque from a front cover to a turbine. The lock-up device includes: a piston that can be frictionally coupled to the front cover; a drive plate fixed to the piston; a plurality of torsion springs supported by the drive plate; and a driven plate elastically coupled to the piston and the drive plate by the plural torsion springs in a rotational direction. The driven plate is fixed to the turbine.
Further, as described in Japanese Laid-open Patent Application Publication No. JP-A-2010-48291, a lock-up device of so-called a multi-plate type using a plurality of clutch plates has been also proposed for increasing the clutch capacity of the lock-up device.
The lock-up device described in Japanese Laid-open Patent Application Publication No. JP-A-2010-48291 includes: a clutch portion disposed between a front cover and a turbine; a power transmission plate coupled to an output member of the clutch portion; and a plurality of torsion springs configured to elastically couple the power transmission plate and the turbine. The clutch portion includes a plurality of clutch plates and a piston disposed between the front cover and the plural clutch plates.
When hydraulic pressure is supplied to the back of the piston, the piston is moved toward the plural clutch plates. The clutch plates are thereby pressed against each other. Accordingly, a lock-up state (power transmitted state) is produced. Under the condition, torque from the front cover is transmitted to the power transmission plate through the clutch portion, and is further transmitted to the turbine through the plural torsion springs.